There have been few reports on the use of oxygen to achieve high selectivity in the oxidative dehydrogenation of alkanes. Alkanes are generally much less reactive than the dehydrogenation products, such as alkenes, dienes, or aromatics. Because of the high temperatures required to activate alkanes, their dehyrogenated products react rapidly with oxygen to form combustion products. Production of useful products by oxidative dehydrogenation of alkanes has therefore usually been limited to the production of oxidized derivatives, viz. aldehydes or organic acids.
Metal oxides have been used as catalysts for dehydrogenation of hydrocarbons. Magnesium oxide is known to be selective for dehydrogenation but its activity is very low for this purpose. Stepanov, et al. (1981). On the other hand, vanadium oxide is active for the oxidation of butane, but its selectivity is only about 10%. Mori, et al. (1983); and Bretton, et al. (1952).
Magnesium vanadale (V-Mg-O) catalysts have been tested for a few oxidative dehydrogenation reactions. A V-Mg-O catalyst was found to be selective for the conversion of ethyl benzene to styrene. Oganowski, et al. (1984); and Hanuza, et al. (1985). This catalyst was also found to be selective for conversion of butene to butadiene. Simakov, et al. (1985). The active compound was identified by Hanuza et al. (1985) as magnesium orthovanadate; MG.sub.3 (VO.sub.4).sub.2.
As far as is known, there have been no reports on the use of magnesium orthovanadate or other V-Mg-O catalysts for dehydrogenation of alkanes. Similarly, no such references are known for the corresponding V-Zn-O catalysts. Certain other metal oxide catalysts have been shown to exhibit some selectivity for conversion of alkanes to unsaturated hydrocarbons, viz. Mg-Mo-O, Ni-Mo-O, and Co-Mo-O catalysts. See Stepanov, et al. (1981); and Doroschenko, et al. (1982). It has also been found that V-P-O catalyzes the oxidation of butane to maleic anhydride. Hodnett (1985).
The selective oxidative dehydrogenation of alkanes has remained a challenging problem. Under conditions which activate the alkanes, reactions may be expected to proceed to oxygenated products such as aldehydes or organic acids, and/or to the partial or complete combustion, forming CO or CO.sub.2. These considerations have probably operated as counter-incentives to research on the production of unsaturated hydrocarbons from alkanes.